So you know you have a recessive trait. So all of the F1 generation are hetero , that is to say that they are carriers of the trait. You didn't say how many offspring you got from the clutch that gave you the homo recessive offspring. At least now you know that you can cross back the new snake with the original and get 100% back snakes with that trait, provided that they are not the same sex. Or you can cross the F2 back with one of the F1's and you should get about a 50% ratio of the homo recessive snakes if it is a single gene that is causing the mutation.

Best of luck with that.

I do have a question you you. What did you do with the normals that you got from the F1 generation? Did you keep them or just sell them off as normals? It also might be nice to see what the F1 normals looked like as adults. Are they black with no pattern showing? What color are their eyes?